The present invention relates to a diaphragm pump. This type of pump is particularly intended for use with analysis instruments, although it can also be used in other fields of application which have corresponding pump requirements.
In respiratory care, pumps are used in conjunction with gas analysis to draw a small flow of sample gas on the patient circuit to an adjacent analysis instrument for analysis. In this case, the pump shall generate a sample flow rate normally in the order of 50-200 ml/min. A pump used in this connection is required to be highly reliable and highly efficient, to have a small size and a low price and to generate only small pulsations with respect to rate of flow, and only small vibrations. It shall also be possible to control the rate of flow through the pump, regardless of pump orientation.
Mainly three types of pumps have been used together with analysis instruments of the aforesaid kind, namely diaphragm pumps, piston pumps and lamella pumps.
A diaphragm pump is based on a construction in which one of the walls of a chamber consists of a moveable diaphragm. The pressure in the chamber can be caused to oscillate, by actuating the diaphragm with the aid of an oscillating lever arm, for instance. The oscillating pressure can be caused to generate a pulsating flow, by providing the chamber with two one-way valves, check valves. In the most common type of diaphragm pump, the type used in aquariums, the oscillating movement is generated with the aid of an electromagnet or solenoid which is powered by alternating current and actuates a lever arm fitted with a permanent magnet. Although this type of diaphragm pump is highly reliable, it has low efficiency. Furthermore, the pump is relatively large and has a low price. Furthermore, this type of diaphragm pump generates relatively large pulsations with respect to flow rate, and also generates heavy vibrations.
The piston pump will normally include an electric motor which drives a piston working in a chamber, through the medium of an eccentric. The chamber is provided with two one-way valves, so as to enable a pulsating flow to be generated. The most serious drawback with the piston pump is that the load on the motor varies over one revolution, meaning that wear on the motor bearings is uneven. Consequently, motors of very high quality are required in order to obtain a satisfactory length of life in respect of this kind of pump. In summary, the piston pump is characterized by low reliability, high efficiency, a relatively small size, a high price, relatively large flow pulsations, and small vibrations.
Lamella pumps are based on a rotor that includes a plurality of lamellae. The rotor is positioned in a circular chamber that includes a conveniently placed inlet and outlet passage-way, and a pulsating flow can be generated as the rotor rotates. The function of the pump is based on sealing contact of the lamellae with the chamber walls as the rotor rotates, in which lies the greatest weakness of this type of pump owing to the fact that the lamellae become worn as a result of the friction against the chamber walls. However, this type of pump has the advantage of being able to generate flows that pulsate less than the flows relating to the two afore-mentioned types of pump. The lamella pump is characterised by low reliability, high efficiency, a relatively small size, a high price, small flow pulsations and small vibrations.
An object of the present invention is to provide a pump that combines the desirable characteristic features of the afore-described types of pump but does not have the their drawbacks.
This object is achieved with an inventive double-acting diaphragm pump in which two symmetrically positioned diaphragms are caused to oscillate through the influence of two counter-directional electric coils.
In the case of an inventive diaphragm pump that includes components that move about a symmetry plane, there is obtained a pump that will generate only extremely low vibrations and thereby obviate the need for separate vibration damping means, therewith resulting in lower costs and also in smaller space requirements.